Two-way intercommunicating loudspeaker system for power circuits



April 19, 1938.

S. J. LEVY TWO-WAY INTERCOMMUNICATING LOUDSFEAKER SYSTEM FOR POWER CIRCUITS Filed May 25, 1936 :YTTORNEY.

Patented Apr. l 9, 1938 PATENT orrics TWO-WAY ildTERCOMMUNICATING LOUD-- SPEAKER SYSTEM FOR. POWER-CIRCUITS Sol- J. Levy, New York,

N. Y., assignor to International Carrier-Call and Television Corporation, a corporation of New York Application May 23', 1936, Serial No. 81,350

6 Claims.

This invention relates to two way communica-' ,tion, and more particularly to carrier frequency communication apparatus andsystems operating 'on electric networks or other metallic transmission'media.

One ofthe objects of my invention is to provlde a universal, highly efiicient, two-way communication system, instantly operable by merely plugging into any -A. C. or D. C. electrical power line circuit and which can be built cheaply and operated with simplicity; and so compact and light in weight as to be readily portable. A-second object of my invention is to provide a novel method of loud speaker inter-communication over the electrical power line circuits from point to point without the use of a microphone,

utilizing the same loud speaker for both transmission and reception. Obviously this system is to operate both interior and exterior to a meter box, namely, for both inter-room or office use and point .to point use on a common power net'- work.

A third object of my inventionis to provide novel effective means of filtering and eliminating all extraneous and. power line noises or interferences, including such inherent noises as D. C. commutator ripples and 60 cycle hums, by coupling the modulated carrier frequency output to the power line circuit through an effective bridge and condenser. filter network, thus accomplishing absolutely quiet two-way loud speaker communication andmaintaining quality of tone and fidelity of'speech, without distortion orrattennation, with a maximum of output volume, and thus permitting housing of both transmission and reception in one small compact unit.

Other objects, and the manner in which the same are obtained, will appear from the following description.

My system as herein described, is generally applicable to line wire systems, such as telephone, electric light, power, and other lines including metallic rails, and I intend no limitations upon theuses to which my invention may be applied.

- My invention will be more clearly understood by reference to the accompanying drawing which illustrates a diagrammatic view of one arrangement of apparatus and circuits embodying the improvements of my invention, illustrating the use of 'a loud speaker as both transmitter and receiver, together with a remote power line control switching, signalling and indicating means.

Referring to the drawing, which shows a preferred embodiment of my invention, it will b-seen (c1. mo -2.5)

that the objects of my invention are accomplished by a novel unitary circuit arrangement acting both as a transmitter and a receiver; Used as a transmitter, by impressing a radio frequency carrier wave of predetermined frequency on the 5 electric power line by means of a stable oscillator circuit in any manner well known to the radio art, and then amplifying the voice by means of a voltage amplifier coupled to a modulation means, thus. modulating the carrier wave frequency, the output of which is coupled tov the power line through a bridge and condenser filter network; and then by means of a selector switch system, utilizing the same tubes for receiving, a highly efiicient two-way loud speaker power line communicating system is provided in one small portable unit. a From the following detailed description of the circuit arrangement, it will be obvious to those "skilled in the art how the foregoing is accomplished.

In transmitting: For transmission purposes, the switch indicated at S in'the drawing and comprising the bridging members sl, s2, s3, s4, s5, and s6, is rotated clockwise one step from the position shown in the drawing. An electronic tube V2 is used for the dual purpose of oscillator and modulator. Grids I and 2, together with an oscillator transformer 00, accurately tuned and adjusted, are used as an oscillator stage to furnish a carrier wave, whose frequency may be in the low intermediate frequency spectrum. Grid 4 is used as a modulator grid upon which is impressed the output voltage from the tube VI,

which is used as a voltage amplifier for the microphone currents generated by the voice. The carrier wave is coupled to thelmodulator through the electron stream of the tube V2 in such a way that the output of the tube V2 is a modulated carrier wave. This component is' now'selected by a very accurately tuned and adjusted resonance system, composed of a selective tuned inters'tage coupling transformer IC, feeding the modulated-carrier wave. to the input grid CG of the tube V3, which is used as an output stage, amplifying this signal and feeding it to the power line through a double-tuned output transformer I OT. The coupling of the output transformer'oT to the load may be accomplished by any one of several different network methods. To permit a maximum power transfer to the power line, and to reduce the clicks and noise reproduction, due to intermittent-contacts in external circuits, the condensers C 1, C2 and CIS are used to make the fier tube V4, which is connected across the power line L, as well as hum pick-up in the loud speaker voice coil VC, which is being used as a microphone, is eliminated by the use of an R. F. choke RC, connected in series with the rectifier plates P P5.

1 Through the selector switch system contact A, the tube VI control grid CG, is connected by contact AT and switch bridging member sl, to the loud speaker used as a microphone through speaker transformer ST, the return connection being left grounded. The V2 oscillator grid I is connected by contact D and switch bridging member 83 to the oscillator coil grid condenser Cl2, by contact DT, and grid leak R10 shunts grid resistor R9. Through contact E to ET and switch bridging member.s2, the V2 circuit is made very sensitive to impulses on the modulator grid 4, by shorting out a portion of the bias resistor R8, to prevent grid rectification during the positive swing of the grid voltage, which when sufiicient in voltage on transmitting to give full modulation without grid current, is not enough on receiving to give a satisfactory output. The V3 control grid CG, is connected by contact B and switch bridging member s5,

through contact BT, to the grid end of the interstage coupling transformer 10, the return connection being left grounded. Through contact C to CT and switch bridging member s4, the V3 plate P3 is connected to the output transformer OT, though condenser CIB, the return connection being left grounded. Through contact F to FT and switch bridging member 86, the condenser Cl9 is shunted by condenser C2 to change the impedance of the putput circuit.

When the switch S is positioned for transmission, it will appear that the high frequency generator or oscillator and the amplifier tubes are electrically connected as components of a transmission circuit. This places the loud speaker 15 in a position to function as a translating device or an audio sound pickup. The audio frequencies are impressed upon VI which serves as an amplifier of the voice frequencies by the action of the speaker as a translating device.

The output of VI or the amplified voice frequencies are fed into the grid 4 of the tube V2, which functions as ahigh frequency.oscillator and which ismodulated by the voice frequencies received from amplifier tube VI. The audio modulated carrier output of the tube V2 is coupled to the grid CG of the tube V3 through'the contacts BT and B and bridging member $5 of the switch S. The output tube V3 is fed through the circuit system OT to the lines by means of plug P. In other words, in transmitting position the output of tube V3 is coupled to 'the metallic transmission media or power line through the circuit, from the plate P3 through the condenser CIG to the contacts CCT and bridging member s4 of the switch S, thence to the condenser CH of the coupling means OT and thence through such means. From the common terminals of condensers CW and CIS connection is made to the ungrounded or high side of the power line through contacts F-FT and bridging member $6 of switch S, condenser C2 and plug P. Connection is made to grounded line through the remaining terminal of condenser Cl9 by direct path through plug P.

When the switch S is in receiving position the modulated carrier frequency passes from the me tallic media or power line through the plug connection P.

The live side of the line through plug P is connected through condenser Cl and contacts F-FR and bridging member s6 1 of switch .8 to the common terminals of condensers C|8 and Cl9. The remainihg terminal CIS as before connects with the grounded line at plug P. Coupled circuit system OT now serves as aninput transformer. The incoming modulated carrier frequencies received from the lines via plug P pass through system OT to the circuit containing condenser CIT. One terminal of CH connects through condenser Cd, contacts DR-D and bridging member" s3 of switch S to the control grid 1 of tube V2 which now functions as a diode detector, rectification taking place between cathode K2 and grid l. The audio frequency components arethen passed through contacts D-DR and bridging member s3 of switch S, resistance Hi3, condenser C5, contacts ARA and bridging member sl of switch S to control grid CG to tube Vi which functions as an audio frequency amplifier. The amplified output is passed from plate Pl through filtering system C9, Clo, R4, R5, and R6, thence through condenser C22 to contacts BR-B and bridging member of switch S to control grid CG of the tube V3 which serves as a second audio frements or offices in the same building. This results from the fact that the meter M, installed by the power companies at the inlet from the feeder line L, to each residence, ofilce or building, serves substantially to prevent control impulses and/or the "carrier wave frequency applied to the lighting system in one residence, office or building from affecting similar apparatus located in another residence, ofiice or building.

The basis of this expedient may be applied generally to arbitrarily section off a line for remote control and/or communication purposes by insertion of small inductances between line sections it isthus desired to isolate.

By shunting the proper capacity condensers MCMC', across the meter terminals M,Figure 1, the blocking effect of the inductance of the meter winding will be obviated, thus permitting transmisslon and control beyond the meter.

By impressing the proper carrier-wave frequency, such a frequency being selected to overcome the blocking effect of any anticipated or predetermined line load impedances, on to the electric power line circuit L, and by providing sufficient power in the oscillator output, the carrier wave frequency can be conveyed beyond the inductance in the meter M, or line blocking means, onto the power feeder lines L, thus carrying communications anywhere on the power and/or lighting lines.

The drawing shows a jack J, so inserted in the output circuits by connections to the selec tor switch S, that when it is desired, one may insert a plug, attached to a pair of head phones into the jack J. and disconnect the loud speaker 'LS. when the selector switch is in receiving position R. q

I wish it to be understood that I do not desire to be limited to the exact details of construction and design as shown, for obvious modifications of the invention within the scope of the appended claims may occur to a man skilled in the art.

.Having thus described my invention, what I claim and desire to secure by United States Letters Patent, is:

1. A two-way loud speaker communicating apparatus for use on electric power line circuits and other metallic transmission media, comprising a carrier frequency oscillator, means including a translating device for modulating said carrier frequency, means for amplifying said modulated carrier frequency, means including switching means, for coupling the output of said amplifying means to said metallic transmission media, or for coupling the metallic transmission media to the input of said modulating means and for switching said translating device from said modulating means into the output of said amplifying means, whereby said modulated carrier frequencies received from said metallic 'transmission media, are detected and reproduced in said translating device.

2. A two way carrier frequency communication system for use on electric power line circuits and other metallic transmission media, compris- I ing in combination a carrier frequency oscillator, means including amplifying means and a translating device for modulating said carrier frequency oscillator, means including a switching means for connecting the output of said oscillator to said metallic transmission media, or for connecting the metallic transmission media to the input of said modulating means and for switching said amplifying means and translating device into the output of said modulating means whereby the modulated carrier frequencies received from said metallic transmission media are demodulated and reproduced in said translating device.

'3. A two way loud speaker communicating apparatus for use on electric power circuits and other metallic transmission media, comprising, in combination, a carrier frequency oscillator, means including a translating device for modulating said carrier frequency, means for amplifying said modulated carrier frequency, means, including switching means, for coupling for transmission purposes the output of said amplifying means to said metallic transmission media, and for coupling for reception purposes the metallic transmission media to the input of said modulating means and for switching said translating device from said modulating means into the output of said amplifying means, whereby said modulated carrier frequencies received from said metallic transmission media are detected and reproduced in said translating device.

4. Aunitary transmitting and receiving carrier frequency communication apparatus for use on electric power line circuits and other metallic transmission media comprising in combination common means for both transmission and reception, said means including a carrier frequency oscillator, means including amplifying means and a translating device for modulating said carrier frequency oscillator, means including switching means for connecting for-'transmission purposes the output of said oscillator to said metallic transmission media, and for connecting for reception purposes the metallic transmission media to the input of said modulating means and for switching said amplifying means and translating device into the output of said modulating'means, whereby the modulated carrier frequencies received from said metallic transmission media are demodulated and reproduced in said translating device.

-5. In a signaling device adapted for both transmission and reception, the combination comprising a modulator-oscillator, an audio frequency amplifier coupled to the input thereof, a microphone coupled to the input of the audio frequency amplifier, a radio frequency amplifier coupled to the output of the modulator-oscillator, and means including switching means connected to the coupling means for conditioning them so that the oscillatoremodulator becomes a detector connected to the input of the audio frequency amplifier, the radio frequency amplifier is coupled to the output of the audio frequency amplifier and the output of the radio frequency amplifier is connected to the microphone, whereby the microphone becomes a loud speaker.

6. In a signaling device adapted for both transmission and reception, the combination comprising a modulator-oscillator, an audio frequency amplifier coupled to the input thereof, a microphone coupled to the input of the audio frequency amplifier, a radio frequency amplifier coupled to the output of the modulator-oscillator, means including switching means connected to the coupling means for conditioning them so that the oscillator-modulator becomes a detector connected to the input of the audio frequency amplifier, the radio frequency amplifier is coupled to the output of the audio frequency amplifier and the output of the radio frequency amplifier is connected to the microphone whereby the microphone becomes a loud speaker, and a low radio frequency impedance network for coupling the output of the radio frequency amplifier to a transmission line and for coupling the transmission line to the input of the modulatoroscillator for transmission and receptionrespec- I s01. J LEVY 

